Sea Level Questions Continue

Yesterday, I read a piece in our local newspaper discussing the problems rising sea level will cause.   Built into the article were two assumptions, both of which are probably  incorrect.

  • Assumption 1 – Sea level could rise by as much as a meter by the year 2100
  • Assumption 2 – Man can take actions to alter this in some significant way.

When I look at sea level data I see confusion.   Today was no exception.   My inquiry began with a look at Satellite data courtesy of  Colorado University.

Sea level, according to CU, is rising at a rate of about 3.2 millimeters a year (plus or minus 12.5%).  That’s about an 1/8 of an inch per year or about a foot per century.  Plus or minus an inch or two.  Not exactly a meter, but coastal regions will have difficulties.  Sea level has been rising since the Little Ice Age ended some 250 years ago.   If I had land in Key West, I’d be worried.

But sea level in Key West isn’t rising at 3.2mm/yr, it’s rising at 2.24 mm/yr.  And the trend has been steady for the 100 years of the data.

chart: Mean Sea Level Trend, 8724580 - Key West, Florida

Key West may be under water at some date in the future, but the rate of change appears to be much less than predicted by IPCC scientists.  I suppose Key West could be an oddity, but it’s unlikely.   I visited the NOAA web site and checked many places I thought might be interesting.   Places like Bermuda, Honolulu, San Francisco, Venice.   Yep, Venice, well Trieste, it’s just across the bay.

http://tidesandcurrents.noaa.gov/sltrends/trends/270-061.png

Trieste’s rate is less than 40% of the Satellite predicted rate.

1.24/3.4 = .397 or 39.7%

The margin for error is half the satellite data rate (.2 mm vs .4mm)

Every place I checked  had a trend rate that was less than the satellite data.   In most cases the predicted margin for error was less than the satellite data too.    A few select data points have a longer history too. I tabulated the results

City                                            rate of change       data history

San Francisco                             2.01 mm/yr       160 years                                              Honolulu                                       1.50 mm/yr       110 years                                                     New York                                     2.77 mm/yr       120 years                                                 Bermuda                                       2.04 mm/yr         70 years                                          Narvik, Norway                       -2.06 mm/yr          60 years                                          Cochin, India                              1.71 mm/yr          70 years                                                Hong Kong                                  2.92 mm/yr          60 years                                        Nagasaki, Japan                        2.20 mm/yr         45 years                                          Sydney, Australia                     0.65 mm/yr         130 years                                     Auckland, New Zealand         1.29 mm/yr         120 years

This data doesn’t tell the full story of the confusion.  Individual sites provide lots of conflicting data.   Honolulu has been trending down since about 2002:

chart: Mean Sea Level Trend, 1612340 - Honolulu, Hawaii

The NOAA presentation of the Bermuda data a bit odd:

chart: Mean Sea Level Trend, 2695540 - Bermuda,

Most of the increase shown in Bermuda happened before 1960.  Had the data set begun in 1955 instead of 1934 the trend line would have shown nearly no net change.  Sea level rose fairly rapidly from 193o until 1955 and has been relatively stable since then.  Go figure.

Virtually every city I checked showed a less ominous looking trend line than the satellite data.  This land based data has it’s limitations.   Many international cities have tiny data sets, particularly in South America and Africa.   Only one data point exists for all of Antarctica

chart: Mean Sea Level Trend, 999-003 - Argentine Islands, Antarctica

I would argue that the Antarctica data doesn’t really suggest a trend but NOAA calculates the trend at  1.43mm/yr.  When I look at the data I see no net changes since 1960.  Sounds kind of like Bermuda’s data to me?

Something is wrong.   Every land site I checked showed less overall change than the satellite data.   How can that be?   The satellite data is an average for the whole world.   Some specific locations should be higher and some places should be lower.

Northern locations like Alaska and Norway are showing reduced sea level due to reduced gravitational pull from the Arctic Ice Sheet (presumably).  Where are the equatorial places that are compensating for that reduction?   I can’t make sense of the data.   Satellite data and measurements at land interfaces don’t tell the same story.

Sea level is extraordinarily difficult to calculate.   Sea level changes in one part of the world can take years and years  to impact the ecosystem.  I understand that storms and changing ice sheets impact the data.  Change that can take decades to correct.

WHY is the satellite data very nearly ALWAYS significantly higher than the land data?

The Satellite data has been higher every year since the data began in 1993.   Every year! Most places I have checked disagree by about 1 mm per year.  After 20 years of data the sources disagree with each other by about 20 mm.  or about .78 inches.  The longer this condition exists, the less I trust the data sets.

It really is difficult to make accurate predictions about sea level if you don’t have the ability to accurately graph the underlying trend line.  Sea level, almost certainly,  has been rising since the end of the Little Ice Age some 250 years ago.  But by how much?   Almost no statistical data exists before the Civil War. I suspect SWAG.

Sea level has been steadily rising for probably 250 years.   How much has been man’s impact? I don’t know and I’ll go a step further…nobody knows!

I am not convinced that we have the tools necessary to accurately predict the future course of events as it relates to sea level.    Sea level appears to be an indicator that follows rather than leads climate change.   How much of today’s changes in sea level were impacted by global temperatures of 20 or 50 or 100 years ago?  I don’t know.  I see guessing here, there and everywhere.

IPCC scientists might have the trends right….but even that is…I fear …. a guess.

 

 

 

 

 

 

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